1. Field of the Invention
The present invention relates to a rare probability connection call registration method for a mode switching system, and more particularly, to an improved rare probability connection call registration method for a mode switching system which is capable of using automatic congestion level (ACL) information within a release message.
2. Description of the Conventional Art
The phenomenon of traffic congestion of a communication network mostly occurs due to an overload in a receiving system. This communication congestion or the overload of the switching system occurs when many call services are requested at one time and therefore, communication traffic concentrated on a specific receiving system results in an unexpected communication failure.
When calls are concentrated at a predetermined time with respect to a specific receiving system (for example, reservations for public performance, or an audience response rating for a television program), the above-described heavy call concentration phenomenon may occur even when an operator of the switching system predicts such heavy call congestion if some special operations for the system is not made.
When a call request is heavily concentrated on a predetermined receiving number, when a large number of calls is concentrated on the destination beyond the design specification of the connection Admission Control function, the system can only offer limited service, and the system may go down due to the above-described problems.
FIG. 2 is a graph illustrating a performance variation when a switching system is overloaded.
As shown therein, the line "a" indicates a theoretical system performance which is obtainable when an overload of the system occurs or traffic congestion occurs, the curved line "c" denotes a system performance when the congestion control function is not operated, and the line "b" denotes the affordable system performance when the congestion control function is operated.
If the above-described situation is maintained, the system congestion resulting from many call attempts concentrated on a specific number may cause further congestion in a neighboring system. So, finally, there may occur system-wide failure.
In order to overcome the above-described problems, a conventional public switched telephone network (PSTN) is directed to check a traffic completion ratio with respect to an input candidate code (the traffic received for a specific code of a predetermined system), and when a call completion ratio of a corresponding code is less than a predetermined threshold value, the call with respect to the corresponding code is controlled.
That is, such method is directed to maximizing the efficiency of the network so that a call system resource may be evenly distributed except for the congested call by detecting a receiving code in which the call completion ratio is lower than that of a normal call, and controlling at least one of the receiving code in a transmitter in which a desired call attempt is possible or the switching system near a transmitting terminal. A call for which the completion ratio is lower is called a rare probability connection call (RPCC).
For a conventional PSTN, control with respect to the code in which the call completion ratio is much lower due to the congestion of a specific switching system is performed based on a result of statistical function after a lapse of a predetermined time after the congestion has occurred, so that a large amount of time is required for the control, and since the call completion ratio is controlled by only statistical data, if faults in the statistical function occur, an error may occur in the system.
In addition, when performing a function based on the candidate code, since the control is performed after a predetermined time after the operator inputs a predetermined code, it is impossible to prevent the call concentration problems due to unpredictable and sudden failure of the system in conventional methods.